The structural system consists of columns, spandrel beams and diagonal cross-braces to form an exterior tube. This design made it possible to build the tower at the same cost as that of a traditional 40-story building. The powerful X bracing on the face of the building made John Hancock Center one of the first skyscrapers to express its structural system. The tower has over 300,000 square feet of commercial space, eight levels of parking, 25 office floors, and 700 apartments. The tapered design provides over 50,000 square feet of area per floor at the base (appropriate for offices), and only 16,000 square feet at the summit (proper for apartments). The Hancock's tapered design accommodates garages and commercial and office space on the lower levels, which require large unobstructed floor areas. The apartments on the upper floors are prime units with spectacular views high above the Chicago streets. Discovering a potentially long-term energy-wasting situation, an estimated $2.5 million was spent on airlocks, energy management computers, and a variable air-volume system. Building amenities include multiple restaurants, health clubs, a swimming pool on the 44th floor, and an ice-skating rink. The building uses 50 elevators which are shared amongst residents and office workers. When completed in 1969, the 1127-foot Hancock Center was second in height worldwide only to the Empire State Building. Aside from the Empire State Building (1931, 1250 feet) and the Chrysler Building (1930, 1046 feet), the Hancock Center is the only building built before 1970 that still ranks among the world's 20 tallest buildings. Big John' as it is dubbed by Chicago natives, currently stands 12th tallest worldwide.' Source: www.lehigh.edu/ctbuh/bom_jhc.html / The Creator's Words: 'The design of the John Hancock Center, in Chicago, was influenced by its unique site. Just off Lake Shore Drive, it is surrounded by huge, residential high-rise buildings and yet faces one of the city's most attractive commercial streets. John Hancock insisted on producing a tall building with residences above, offices and commercial uses below. The search for a new kind of structure which would accommodate multiple uses and also express the scale and grandeur of a one-hundred-story tower, led Dr. Kahn and me to the diagonal tube. It was as essential to us to expose the structure of this mammoth as it is to perceive the structure of the Eiffel Tower, for Chicago, honesty of structure has become a tradition.' Source: www.GreatBuildings.com/buildings/John_Hancock_Center.html